EPA Facts about Uranium
What is uranium?
Uranium is a radioactive metal that is present in
low amounts in rocks, soil, water, plants, and
animals. Uranium and its decay products
contribute to low levels of natural background
radiation in the environment. Significant
concentrations of uranium occur naturally in
some substances such as phosphate deposits
and uranium-enriched ores.
How does uranium change in the
environment?
Natural uranium is found in the environment in
three forms, called isotopes: uranium-234,
uranium-235, and uranium-238. Ninety-nine
percent of natural uranium occurring in rock is
uranium-238. Uranium-235 accounts for just
0.72 percent of natural uranium, but it is more
radioactive than uranium-238. Uranium-234 is
the least abundant uranium isotope in rock.
Uranium is not a stable element. As uranium
decays, it releases radiation and forms decay
products. Uranium-238 decay products include
uranium-234, radium-226, and radon-222. See
"EPA Facts about Radon and Radium" for
additional information on these radionuclides.
Natural uranium releases alpha particles and low
levels of gamma rays. Alpha particles can travel
only short distances and cannot penetrate
human skin. Gamma radiation, however, can
penetrate the body.
The time required for a radioactive substance to
lose 50 percent of its radioactivity by decay is
known as the half-life. The half-life for uranium-
238 is about 4.5 billion years, uranium-235 is
710 million years, and uranium-234 is 250,000
years. Because of the slow rate of decay, the
total amount of natural uranium in the earth
stays almost the same, but radionuclides can
move from place to place through natural
processes or by human activities. Rain can wash
soil containing uranium into rivers and lakes.
Mining, milling, manufacturing, and other
human activities also release uranium to the
environment.
What are the uses of uranium?
Uranium-235 is used in nuclear weapons and
nuclear reactors. Depleted uranium (natural
uranium in which almost all of the uranium-235
has been removed) is used to make ammunition
for the military, guidance devices and
compasses, radiation shielding material, and X-
ray targets. Uranium dioxide is used to extend
the lives of incandescent lamps used for
photography and motion pictures. Very small
amounts of other uranium compounds are used
in photography for toning, in the leather and
wood industries for stains and dyes, and in the
wool industries. Uranium has also been used in
the past in ceramics as a coloring agent.
How are people exposed to uranium?
Uranium-238 and members of its decay chain,
which include uranium-234, radium-226, and
radon-220, are present in nature. The members
of the decay chain in undisturbed soil are
present, often at concentrations that
approximate that of the parent uranium-238.
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Uranium ore contains all the daughter elements
of uranium-238 and uranium-235, but the
uranium-238, uranium-234, and uranium-235
are extracted and chemically separated during
processing. This concentrated uranium product,
which is generated at uranium mill tailing sites
and uranium processing facilities, is a potential
source of exposure to individuals and the
environment and is a primary concern for
cleanup of these sites. Potential individual
exposure at these sites may be from different
pathways, but the groundwater pathway is of
particular concern because of the mobility of
uranium.
How does uranium get into the body?
Uranium can enter the body when it is inhaled
or swallowed or through cuts in the skin. About
99 percent of the uranium ingested in food or
water will leave a person's body in the feces,
and the remainder will enter the blood. Most of
this uranium will be removed by the kidneys and
excreted in the urine within a few days. A small
amount of the uranium in the bloodstream will
be deposited in a person's bones, where it will
remain for several years.
Alpha particles released by uranium cannot
penetrate the skin, so natural uranium that is
outside the body is less harmful than that which
is inhaled, swallowed, or enters through the
skin. When uranium gets inside the body,
radiation and chemical damage can lead to
cancer or other health problems, including
kidney damage.
Is there a medical test to determine
exposure to uranium?
Tests are available to measure the amount of
uranium in a urine or stool sample. These tests
are useful if a person is exposed to a larger-than-
normal amount of uranium, because most
uranium leaves the body in the feces within a
few days. Uranium can be found in the urine for
up to several months after exposure. However,
the amount of uranium in the urine and feces
does not always accurately show the level of
uranium exposure. Since uranium is known to
cause kidney damage, urine tests are often used
to determine whether kidney damage has
occurred.
How can uranium affect people's health?
In addition to the risks of cancer posed by
uranium and all other radionuclides, uranium is
associated with noncancer effects, and the
major target organ of uranium's chemical
toxicity is the kidney. Radioactivity is a health
risk because the energy emitted by radioactive
materials can damage or kill cells. The level of
risk depends on the level of uranium
concentration.
What recommendations has the U.S.
Environmental Protection Agency made
to protect human health?
Please note that the information in this section
is limited to recommendations EPA has made to
protect human health from exposure to
uranium. General recommendations EPA has
made to protect human health at Superfund
sites (the 10~4 to 10"6 cancer risk range), which
cover all radionuclides including uranium, are

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summarized in the fact sheet "Primer on
Radionuclides Commonly Found at Superfund
Sites."
EPA has established a Maximum Contaminant
Level (MCL) of 30 micrograms per liter (|_ig/liter)
for uranium in drinking water. For uranium mill
tailing sites, EPA has established 30 picoCuries
per liter (pCi/L) for uranium-234 and -238 as
standards for protecting groundwater. The EPA
document "Use of Uranium Drinking Water
Standards under 40 CFR 141 and 40 CFR 192 as
Remediation Goals for Groundwater at CERCLA
Sites" provides guidance regarding how these
two standards should be implemented as an
Applicable or Relevant and Appropriate
Requirement (ARAR) at Superfund sites. This
document is available online at:
http://www.epa.gov/superfund/health/contami
nants/radiation/pdfs/9283 1 14.pdf.
Also for uranium mill tailing sites, EPA has
established 5 picoCuries per gram (pCi/g) of
radium as a protective health-based level for the
cleanup of the top 15 centimeters of soil. These
regulations under 40 Code of Federal
Regulations (CFR) Part 192.12 are often ARARs
at Superfund sites. The EPA document "Use of
Soil Cleanup Criteria in 40 CFR Part 192 as
Remediation Goals for CERCLA Sites" provides
guidance to EPA staff regarding when 5 pCi/g is
an ARAR or otherwise recommended cleanup
level for any 15 centimeters of subsurface soil
contaminated by radium other than the first 15
centimeters. This document is available online
at:
http://www.epa.gov/superfund/health/contami
nants/radiation/pdfs/u mtrcagu.pdf.
If regulations under 40 CFR Part 192.12 are an
ARAR for radium in soil at a Superfund site, then
Nuclear Regulatory Commission (NRC)
regulations for uranium mill tailing sites under
10 CFR Part 40 Appendix A, I, Criterion 6(6), may
be an ARAR at the same site, particularly if
uranium-234 or uranium-238 is a contaminant at
the site.
Criterion 6(6) requires that the level of radiation,
called a "benchmark dose," that an individual
would receive be estimated after that site was
cleaned up to the radium soil regulations under
40 CFR Part 192.12. This benchmark dose then
becomes the maximum level of radiation that an
individual could be exposed to from all
radionuclides, except radon, in both the soil and
buildings at the site. The EPA document
"Remediating Goals for Radioactively
Contaminated CERCLA Sites Using the
Benchmark Dose Cleanup Criterion 10 CFR Part
40 Appendix A, I, Criterion 6(6)" provides
guidance regarding how Criterion 6(6) should be
implemented as an ARAR at Superfund sites,
including using a radium soil cleanup level of
5 pCi/g in both the surface and subsurface when
estimating a benchmark dose. This document is
available online at:
http://www.epa.gov/superfund/health/contami
nants/radiation/pdfs/pa rt40.pdf.
For more information about how EPA addresses
uranium at Superfund sites
Contact Stuart Walker of EPA:
(703) 603-8748 or walker.stuart@epa.gov,
or visit EPA's Superfund Radiation Webpage:
http://www.epa.gov/superfund/resources/radiation/
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